console.log('学习拖拽')

window.onload = function () {
    var drag = document.getElementById('drag');
    // //点击某物体时，用drag对象即可，move和up是全局区域，
    // 也就是整个文档通用，应该使用document对象而不是drag对象(否则，采用drag对象时物体只能往右方或下方移动)  
    drag.onmousedown = function (event) {
        var event = event || window.event; //兼容IE浏览器
        //    鼠标点击物体那一刻相对于物体左侧边框的距离=点击时的位置相对于浏览器最左边的距离-物体左边框相对于浏览器最左边的距离
        var diffX = event.clientX - drag.offsetLeft;
        var diffY = event.clientY - drag.offsetTop;
        if (typeof drag.setCapture !== 'undefined') {
            drag.setCapture();
        }
        document.onmousemove = function (event) {
            var event = event || window.event;
            var moveX = event.clientX - diffX;
            var moveY = event.clientY - diffY;
            if (moveX < 0) {
                moveX = 0
            } else if (moveX > window.innerWidth - drag.offsetWidth) {
                moveX = window.innerWidth - drag.offsetWidth
            }
            if (moveY < 0) {
                moveY = 0
            } else if (moveY > window.innerHeight - drag.offsetHeight) {
                moveY = window.innerHeight - drag.offsetHeight
            }
            drag.style.left = moveX + 'px';
            drag.style.top = moveY + 'px'
        }
        document.onmouseup = function (event) {
            this.onmousemove = null;
            this.onmouseup = null;
            //修复低版本ie bug  
            if (typeof drag.releaseCapture != 'undefined') {
                drag.releaseCapture();
            }
        }
    }


}